A common problem in fuel cell operation is water management.
In proton exchange membrane (PEM) fuel cells, the polymer electrolyte membrane that conducts the protons and repels electrons can only function properly when it is sufficiently hydrated, so that the incoming gas streams are typically pre-humidified when entering the fuel cell. Furthermore, the so-called electro-osmotic drag effect leads to water being transported through the membrane from the anode side to the cathode side, and the maximum current density that can be drawn from the fuel cell might be limited by the fact that the anode gas dries out.
Water management in fuel cell has been generally investigated by trial-and-error, through a large number of experiments varying cell performance by varying temperature, pressure, stoichiometric flow ratio and the relative humidity of the gases at the respective inlets.
In water balance experiments, the typical approach is to condense the anode and cathode exit gas streams and weigh the amount of liquid water.
This method is reliable. However, it can be very time consuming as it can take many hours to collect sufficient water for a measurement and the error margin is quite high due to partial evaporation of the collected water. Moreover, it can only be applied to fuel cell with a sufficiently large area in order to collect enough water for a reliable water balance.
Importantly, this method is not suitable to be applied to a fuel cell powered vehicle as it cannot provide real time measurement.
It is therefore desirable to have a method for managing water balance in fuel cell which provides more accurate data, and real time measurement, thus enabling to communicate the water balance to the fuel cell controller at any given time.
Hence, an improved method of operating a fuel cell would be advantageous, and in particular a more efficient and/or reliable method for monitoring and adjusting the water balance would be advantageous.